The present application claims priority to, Japanese Application No. P11-345465 filed Dec. 3, 1999, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to an inspection apparatus used for inspecting a device such as a semiconductor integrated circuit or the like which has a micro concave and convex pattern, and an inspection method for inspecting a micro concave and convex pattern.
In recent years, the integration rate of semiconductor integrated circuit has been improved as digitalization has been developed in the electric industrial field. How this highly integrated semiconductor circuit can be efficiently supplied at low costs is a significant problem that will decide future progress in the digital electronic industrial field.
To produce efficiently semiconductor integrated circuits at low costs, it is important to find rapidly a problem which occurs during the manufacturing process, such as a change or the like of a line width of a micro pattern, to find the cause of the problem, and to make an effective countermeasure for the manufacturing equipments or manufacturing process. Therefore, there is a greater demand for an inspection apparatus capable of inspecting a micro pattern.
Known as inspection apparatuses having a high resolution are those using a scanning electron microscope (SEM), an atomic force microscope (AFM), and the like. However, these scanning electron microscopes and atomic force microscopes require vacuum in inspection, and are therefore inconvenient for handling. In addition, it takes much time to inspection entirely a semiconductor device.
In contrast, an inspection apparatus using an optical microscope is advantageous in that inspection can be carried out undestructively without necessitating vacuum or contact. However, the patterns of semiconductor integrated circuits have become more and more micro in recent years, so that the line width have been decreased to 0.18 xcexcm or less. Therefore, it has become difficult for inspection apparatuses using conventional microscopes to measure accurately line widths of the patterns of the semiconductor integrated circuits.
In particular, it is desired that inspection of a pattern of a semiconductor integrated circuit should be carried out with a resist pattern formed on a semiconductor wafer. It is, however, difficult to measure accurately and properly this resist pattern having a micro structure.
The present invention has been proposed in view of the situation as described above and has an object of providing an inspection apparatus and an inspection method capable of inspecting a more micro pattern with high accuracy.
In case where illumination light is irradiated on an inspection target having a concave and convex pattern, such as a semiconductor integrated circuit, to pick up an image thereof, the illumination light diffracted by the concave and convex pattern causes interference so that a light intensity profile corresponding to the concave and convex pattern can be obtained, if the concave and convex pattern of the inspection target is substantially as micro as the wavelength of the illumination light.
If the diffraction efficiency of the concave and convex pattern with respect the illumination light exceeds a predetermined value, a peak corresponding to a boundary portion between a concave portion and a convex portion of the concave and convex pattern appears on the light intensity profile corresponding to this concave and convex pattern. The peak thus appearing on the light intensity profile can particularly be found clearly when reflection light or transmission light of the illumination light from the inspection target is observed in an off-focus state.
Therefore, for example, the reflection light or transmission light of the illumination light from the inspection target is observed in an off-focus state, and a distance between peaks corresponding to boundary portions concave and convex portions from the obtained intensity profile. The width of a concave or convex portion of the concave and convex pattern as the inspection target can be measured accurately on the basis of the distance between peaks.
If the state of a concave and convex pattern is inspected on the basis of a light intensity profile obtained by the diffraction interference of illumination light, it is possible to detect a very micro change of a pattern with accuracy in nano-meter order, advantageously for an inspection apparatus.
The present invention has been proposed on the basis of knowledge as described above, and provides an inspection apparatus comprising: illumination means for illuminating an inspection pattern having a concave and convex pattern with illumination light; image pickup means for picking up an image of the inspection target illuminated by the illumination means; a detection optical system for introducing reflection light or transmission light from the inspection target illuminated with the illumination means, to the image pickup means; and image processing means for preparing a light intensity profile corresponding to the concave and convex pattern of the inspection target, based on the image of the inspection target picked up by the image pickup means. Further, in this inspection apparatus, the detection optical system introduces the reflection light or transmission light in an off-focus state from the inspection target illuminated by the illumination means to the image pickup means, such that the image processing means prepares a light intensity profile having a peak corresponding to a boundary portion between a concave portion and a convex portion of the concave and convex pattern of the inspection target.
That is, in this inspection apparatus, the detection optical system introduces the reflection light or transmission light in an off-focus state, from the inspection target illuminated with the illumination light to the image pickup means, thereby to pick up an image of the inspection target in an off-focus state by the image pickup means. Further, based on the image of the inspection target picked up in this off-focus state, the image processing means prepares a light intensity profile corresponding to the concave and convex pattern of the inspection target. In this manner, a light intensity profile having a peak corresponding to a boundary portion between a concave portion and a convex portion of the inspection target is obtained.
According to this inspection apparatus, a light intensity profile having a peak corresponding to a boundary portion between a concave portion and a convex portion of the inspection target is prepared by the image processing means. Therefore, a very micro change of a pattern can be detected accurately, for example, if the state of the concave and convex pattern, such as a width of a concave or convex portion of the concave and convex pattern, is inspected on the basis of the light intensity profile obtained as described above.
Also, an inspection method according to the present invention comprises steps of: illuminating an inspection pattern having a concave and convex pattern with illumination light; introducing reflection light or transmission light from the inspection target illuminated with the illumination light, to image pickup means, and picking up an image of the inspection target by image pickup means; preparing a light intensity profile having a peak corresponding to a boundary between a concave portion and a convex portion of the concave and convex pattern of the inspection target, based on the image of the inspection target picked up by the image pickup means; and inspecting a state of the concave and convex pattern of the inspection target, based on the intensity profile obtained.
According to this inspection method, it is possible to detect properly a very micro change of a pattern with accuracy of nano-meter order.
According to the present invention, an image of an inspection target having a concave and convex pattern is picked up in an off-focus state by an image pickup element. Based on this image, the image processing means prepares a light intensity profile having a peak corresponding to a boundary portion between a concave portion and a convex portion of the concave and convex pattern of the inspection target. If the width of the concave or convex portion of the concave and convex pattern or the state of the concave and convex pattern is inspected on the basis of the light intensity profiled thus obtained, it is possible to detect accurately a very micro change of a pattern.
Also, in the inspection method according to the present invention, a light intensity profile having a peak corresponding to a boundary portion between a concave portion and a convex portion of the concave and convex pattern of the inspection target is prepared on the basis of the image of the inspection target picked up in an off-focus state. Based on the prepared intensity profile, the state of the concave and convex pattern of the inspection target is inspected, so that a very micro change of a pattern can be detected accurately.